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Manganese-doped ceria nanoparticles were prepared by hydrothermal synthesis and the prepared samples were thermally treated at 500 °C for 2 hours. The samples were investigated using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), energydispersive X-ray spectroscopy (EDS), N2 adsorption and X-ray photoelectron spectroscopy (XPS). XRD revealed that nanocrystalline ceria is the main phase in all samples, while a romanechite-like phase (Na2Mn O5 10) appears in the sample doped with 30% of Mn. TEM coupled with EDS exposed the presence of the same phase in the sample doped with 20% Mn. While ceria particles have spherical morphology and particle size ranging from 4.3 to 9.2 nm, the rare crystals of the romanechite-like phase adopt a tubular morphology with a length of at least 1 μm. However, the decrease in the ceria lattice constant and the EDS spectra of the ceria nanoparticles clearly indicate that a substantial amount of manganese entered the ceria crystal lattice. Manganese doping has a beneficial impact on the specific surface area of ceria. XPS measurements reveal a decrease in the Ce3+/Ce3++Ce4+ content in the doped samples which is replaced by Mn3+. Moreover, a drasticincrease in adsorbed oxygen is observed in the doped samples which is the consequence of the increase in Mn3+ species that promotes oxygen migrations to the surface of the sample. Compared to the pure sample, the doped samples showed significantly higher catalytic activity for the process of toluene oxidation.

Manganese doped nanosized ceria samples were prepared by mechanochemical synthesis. Characterization was done using X‐ray diffraction (XRD), UV‐Vis diffuse reflectance spectroscopy (UV‐Vis DRS), X‐ray photoelectron spectroscopy (XPS) and others. Different conditions of synthesis were tried. Beside cerium carbonate, cerium chloride and amorphous phase remain in the product. Cerium carbonate decomposes around 250 °C, while the decomposition process centered at 330 °C was attributed to cerium chloride decomposition. Along with ceria, birnessite occurs in doped samples after thermal treatment and washing. Ceria lattice constant is reduced from 5.405 Å for pure sample to 5.401 Å for the 30 % doped sample as a consequence of manganese entrance in the ceria lattice. Ceria bandgap is significantly reduced with doping. Particle size was far greater than crystallite size due to a strong tendency toward agglomeration. All prepared powders proved to be efficient catalysts for toluene oxidation with the 30 % doped sample being the most promising.

Lowering the constitutive domains of semiconducting oxides to the nano-range has recently opened up the possibility of added benefit in the research area of sensing materials, in terms both of greater specific surface area and pore volume. Among such nanomaterials, ceria has attracted much attention; therefore, we chemically derived homogeneous ceria nanoparticle slurries. One set of samples was tape-casted onto a conducting glass substrate to form thin-films of various thicknesses, thereby avoiding demanding reaction conditions typical of physical depositions, while the other was pressed into pellets. Structural and microstructural features, along with electrical properties and derivative humidity-sensing performance of ceria thin-films and powders pressed into pellets, were studied in detail. Particular attention was given to solid-state impedance spectroscopy (SS-IS), under controlled relative humidity (RH) from 30%–85%, in a wide temperature and frequency range. Moreover, for the thin-film setup, measurements were performed in surface-mode and cross-section-mode. From the results, we extrapolated the influence of composition on relative humidity, the role of configuration and thin-film thickness on electrical properties, and derivative humidity-sensing performance. The structural analysis and depth profiling both point to monophasic crystalline ceria. Microstructure analysis reveals slightly agglomerated spherical particles and thin-films with low surface roughness. Under controlled humidity, the shape of the conductivity spectrum stays the same along with an increase in RH, and a notable shift to higher conductivity values. The relaxation is slow, as the thickness of the pellet slows the return of conductivity values. The increase in humidity has a positive effect on the overall DC conductivity, similar to the temperature effect for semiconducting behavior. As for the surface measurement setup, the thin-film thickness impacts the shape of the spectra and electrical processes. The surface measurement setup turns out to be more sensitive to relative humidity changes, emphasized with higher RH, along with an increase in thin-film thickness. The moisture directly affects the conductivity spectra in the dispersion part, i.e., on the localized short-range charge carriers. Moisture sensitivity is a reversible process for thin-film samples, in contrast to pellet form samples.

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